Summary:

This PR adds a new root folder type called "Templates". Any document added to this root folder will show up in the "Add Item" menu in the project tree under a new submenu called "From Template". Selecting a template here will create a new document in the selected position in the tree and create a new document with the content copied from the template.

Related Issue(s):

Closes #1125
Closes #996

Reviewer's Checklist:

• The header of all files contain a reference to the repository license
• The overall test coverage is increased or remains the same as before
• All tests are passing
• All flake8 checks are passing and the style guide is followed
• Documentation (as docstrings) is complete and understandable
• Only files that have been actively changed are committed